linux-kernel - Re: [PATCH v7 03/14] usb: hcd.h: Add OTG to HCD interface

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Date:	Wed, 11 May 2016 14:19:09 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Roger Quadros <rogerq@...com>
Cc:	Jun Li <jun.li@....com>,
	"peter.chen@...escale.com" <peter.chen@...escale.com>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"balbi@...nel.org" <balbi@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"jun.li@...escale.com" <jun.li@...escale.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
	"abrestic@...omium.org" <abrestic@...omium.org>,
	"yoshihiro.shimoda.uh@...esas.com" <yoshihiro.shimoda.uh@...esas.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v7 03/14] usb: hcd.h: Add OTG to HCD interface

On Tue, May 10, 2016 at 12:20:28PM +0300, Roger Quadros wrote:
> On 10/05/16 11:03, Jun Li wrote:
> > Hi
> > 
> >> -----Original Message-----
> >> From: Roger Quadros [mailto:rogerq@...com]
> >> Sent: Tuesday, May 10, 2016 3:35 PM
> >> To: Peter Chen <hzpeterchen@...il.com>
> >> Cc: peter.chen@...escale.com; stern@...land.harvard.edu; balbi@...nel.org;
> >> gregkh@...uxfoundation.org; dan.j.williams@...el.com; jun.li@...escale.com;
> >> mathias.nyman@...ux.intel.com; tony@...mide.com; Joao.Pinto@...opsys.com;
> >> abrestic@...omium.org; yoshihiro.shimoda.uh@...esas.com; linux-
> >> usb@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
> >> omap@...r.kernel.org; devicetree@...r.kernel.org
> >> Subject: Re: [PATCH v7 03/14] usb: hcd.h: Add OTG to HCD interface
> >>
> >> On 10/05/16 06:14, Peter Chen wrote:
> >>> On Mon, May 09, 2016 at 12:45:38PM +0300, Roger Quadros wrote:
> >>>> On 06/05/16 12:41, Peter Chen wrote:
> >>>>> On Mon, May 02, 2016 at 03:18:46PM +0300, Roger Quadros wrote:
> >>>>>> The OTG core will use struct otg_hcd_ops to interface with the HCD
> >>>>>> controller.
> >>>>>>
> >>>>>> The main purpose of this interface is to avoid directly calling HCD
> >>>>>> APIs from the OTG core as they wouldn't be defined in the built-in
> >>>>>> symbol table if CONFIG_USB is m.
> >>>>>>
> >>>>>> Signed-off-by: Roger Quadros <rogerq@...com>
> >>>>>> Acked-by: Peter Chen <peter.chen@....com>
> >>>>>
> >>>>> Roger, after thinking more, I still think current dependency between
> >>>>> OTG, HCD and gadget are too complicated. Since the OTG can't work if
> >>>>> it is built as module, I suggest letting OTG depends on HCD &&
> >>>>> USB_GADGET, and it is a boolean, in that case, we don't need to
> >>>>> export any HCD and gadget ops, things will be much simpler.
> >>>>> What's your opinion?
> >>>>
> >>>> How will it work if HCD and USB_GADGET are modules and OTG is built-in?
> >>>>
> >>>
> >>> The OTG will not be compiled at this situation, since it is boolean.
> >>> In fact, like I mentioned at above, OTG or USB function can't work if
> >>> it is built as module.
> >>
> >> Isn't this a limitation?
> >> As per the current implementation dual role works fine even with both
> >> USB_GADGET and HCD as module.
> > 
> > My understand: only make sense for pass build, host can't work before
> > gadget modules loaded; gadget can't work before hcd loaded, nothing
> > can work before all drivers are loaded.
> 
> I can make OTG depend on GADGET and HCD, no issue with that.
> But we can't get rid of the OTG to HCD/Gadged interfaces as we want things
> to work with GADGET and HCD as modules.
> 

Let's make OTG depends on gadget and hcd at Kconfig, and keep others
unchanging, if no one objects it.

Peter
> > 
> >>
> >> In the real world it is unlikely that GADGET and HCD will be built-in.
> > 
> > Why? User enable USB_OTG means both drivers should be enabled anyway.
> 
> Enabled, but not necessarily built-in. Most distributions don't have them
> as built-in.
> 
> But let's not argue in that direction. Let's say that they can be either
> built-in or modules.
> 
> > Even in non-OTG case, both may be built-in for machine with 2 ports
> > (one port is host only, the other one is peripheral only).
> 
> Sure. Every system designer is free to select the configuration.
> 
> > 
> > A general question, 2 drivers depends on each other, allowable?
> 
> I don't thing that's possible. Kconfig will complain.
> http://lxr.free-electrons.com/source/Documentation/kbuild/kconfig-language.txt#L397
> 
> cheers,
> -roger
> 
> >>>>>
> >>>>>> ---
> >>>>>>  include/linux/usb/hcd.h | 24 ++++++++++++++++++++++++
> >>>>>>  1 file changed, 24 insertions(+)
> >>>>>>
> >>>>>> diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
> >>>>>> index b98f831..861ccaa 100644
> >>>>>> --- a/include/linux/usb/hcd.h
> >>>>>> +++ b/include/linux/usb/hcd.h
> >>>>>> @@ -399,6 +399,30 @@ struct hc_driver {
> >>>>>>
> >>>>>>  };
> >>>>>>
> >>>>>> +/**
> >>>>>> + * struct otg_hcd_ops - Interface between OTG core and HCD
> >>>>>> + *
> >>>>>> + * Provided by the HCD core to allow the OTG core to interface
> >>>>>> +with the HCD
> >>>>>> + *
> >>>>>> + * @add: function to add the HCD
> >>>>>> + * @remove: function to remove the HCD
> >>>>>> + * @usb_bus_start_enum: function to immediately start bus
> >>>>>> +enumeration
> >>>>>> + * @usb_control_msg: function to build and send of a control urb
> >>>>>> + * @usb_hub_find_child: function to get pointer to the child
> >>>>>> +device  */ struct otg_hcd_ops {
> >>>>>> +	int (*add)(struct usb_hcd *hcd,
> >>>>>> +		   unsigned int irqnum, unsigned long irqflags);
> >>>>>> +	void (*remove)(struct usb_hcd *hcd);
> >>>>>> +	int (*usb_bus_start_enum)(struct usb_bus *bus, unsigned int
> >> port_num);
> >>>>>> +	int (*usb_control_msg)(struct usb_device *dev, unsigned int
> >> pipe,
> >>>>>> +			       __u8 request, __u8 requesttype, __u16 value,
> >>>>>> +			       __u16 index, void *data, __u16 size,
> >>>>>> +			       int timeout);
> >>>>>> +	struct usb_device * (*usb_hub_find_child)(struct usb_device
> >> *hdev,
> >>>>>> +						  int port1);
> >>>>>> +};
> >>>>>> +
> >>>>>>  static inline int hcd_giveback_urb_in_bh(struct usb_hcd *hcd)  {
> >>>>>>  	return hcd->driver->flags & HCD_BH;
> >>>>>> --
> >>>>>> 2.7.4
> >>>>>>
> >>>>>> --
> >>>>>> To unsubscribe from this list: send the line "unsubscribe
> >>>>>> linux-usb" in the body of a message to majordomo@...r.kernel.org
> >>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>>>>
> >>>

-- 

Best Regards,
Peter Chen